This research project has involved the intensive study of histocompatibility alloantigens on cultured human tumor cell lines with special reference to serological and functional comparative tests for the specificity of alloantigens on lymphocyte subpopulations from tumor donors. We have extensive experience with the HLA-typing of human cell lines, including work with: a large number of available cell lines of diverse origin; normal tissues, fibroblast cell lines, B-cell lines and fresh and frozen peripheral blood lymphocytes from the cell line donors; large numbers of highly selected allospecific HLA typing reagents that collectively define all of the well-characterized HLA-A, B, C, DR, MB and MT antigens; large numbers of completely HLA-typed normal panel cells, B-cell type CLL cells and lymphoblastoid cell lines; and a selection of monoclonal and allospecific antibodies to DR antigens, T-cell differentiation antigens and alloantigens expressed on activated T cells. Our research activities have already helped: (1)\to establish that human tumor cell lines almost always express genetically appropriate HLA alloantigens which usually remain stable during cell culture and can be used to confirm the identity and purity of cell line cultures; (2)\to study the functional role of the DR alloantigens expressed on certain human tumor cell lines, notably melanomas, as primary or secondary stimulators of allogeneic lymphocytes and to thereby help establish that the relationship between HLA-D and HLA-DR determinants, which are defined in relation to primary lymphocyte stimulation and serological reaction patterns, respectively, shows differential characteristics in different cell types; (3)\to establish that the DR alloantigens expressed on certain human tumor cell lines fail to act as stimulators, but do act as targets of cytotoxic allogeneic lymphocytes; (4)\to establish that the allospecificity of sera from patients receiving therapeutic vaccines containing allogeneic cultured tumor cell line extracts are primarily directed against allogeneic HLA antigens instead of tumor-specific antigens. Currently, studies of the role of cell line DR molecules in antigen presentation, the differential expression of other Class II molecules (e.g., DS [MB] and SB) and the possible expression of T cell-specific allogeneic determinants on some melanoma cells are in progress.